Line cutters of a type utilizing a cylinder-contained, explosion-propelled piston having at its forward end a circular cutting edge for severing the load line of a balloon or the reefing line of a parachute, have hitherto been disclosed in patents such as Bohl, U.S. Pat. Nos. 2,924,147; Gross, 2,742,697; Stupian, 2,897,799; and Stott, 2,942,818. The Stott patent also discloses a shear pin, extending through the cylinder wall into the piston, for normally restraining the piston in its retracted position. Other patents disclosing cylinder-contained pistons propelled by detonation of an explosive charge within the cylinder, are Fritz, U.S. Pat. Nos. 3,111,808; Davis, 2,132,148 and Barr, 3,119,302.
Resume of the Invention
An object of the invention is to provide an explosive cartridge which is hermetically sealed and separately fixed inside the cutter cylinder so as to be capable of withstanding environmental conditions with a rugged characteristic.
Another object is to provide an explosive cutter unit having means to securely hold the cutter piston in a retracted position until firing is effected. In one aspect, the piston has a stem projecting rearwardly through a seal ring and attached, as by welding, to the forward end of the explosive cartridge. An alternative construction, utilizing a holding pin of soft material which is readily sheared upon firing, can dispense with the stem for fastening the rear end of the piston to the explosive cartridge, utilizing simply a soft, resilient pad between the rear end of the piston and the forward end of the explosive cartridge for containing the explosive gases.
A further object is to provide a cutter piston of maximum simplicity combined with maximum effectiveness in severing a sleeved wire at diametrically opposite points within its containing cylinder, and in receiving the severed wire slice. To this end, the cutting end of the piston is provided with a deep cavity defined within a conical wall of approximately 60.degree. spread.